HUSNG - What does it mean to play tight?

[Nichomacheo]

In the context of a heads up sit-and-go, where the effective stacks are never above 75...

What does it mean for a player to be tight? Does it mean he isn't raising with a lot of 52s type hands preflop? Does it mean that he isn't c-betting without at least some part of the flop? Does it mean not firing two barrels when he thinks his opponent is weak?

I know this is a very general question, but I honestly don't have a good grasp of what tight means as it applies to HU...